The avocado fell out of favor as a staple across the state's landscapes, and what a shame. It's a classic whose surprising variety and burly magnificence bestow so much more than fruit.

THE avocado tree can't help itself. Plant it in Southern California and it grows high and wide, its limbs like pumped-up biceps looking for room to flex. Its fruit hangs for months and months, like Christmas decorations you wish someone would take down.

Its coloring put the ranch in ranch houses, but who decorates in avocado green anymore? By the time the '70s had passed, so had the tree's popularity as a backyard exotic. The old-timers just got bigger, a sometimes intimidating inheritance when you bought a house in Pasadena or Brentwood or La Habra, a reminder of vanished orchards.

But that Atlas of a tree gushed fruit that, once picked, was green gold, as much as $3 apiece in the market. The limbs were an unparalleled place to put a treehouse, so easy to climb and sturdy. The avocado tree was -- and still is -- Southern California's Southern magnolia, its leaves glossy coasters, forever shedding like tears of joy. Scuffle through them and there is that smell of wild spices.

My friend Susan had an avocado tree in the yard of her first house in Santa Monica. Every morning she looked forward to opening the French doors and seeing that tree, its magnificent armature, its solidity, its promise. A native New Yorker, she had no childhood affinity for the tree's exotic fruit, but its almost mythic proportions were a revelation. "It grounded me," she says.

Avocados in California branch back to Guatemala and Mexico. (The West Indies is another source, but its varieties favor moister Florida.) Mexico's small black avocados -- the Dickinson is an example -- were the first to find favor but were quickly usurped by the mighty Fuerte and Lyon and Anaheim, all butterfly green and much prettier in the fruit bowl.

Then in 1926, the Microsoft of avocados was born. A hobbyist in La Habra Heights produced a new variety, naming it after himself. The Hass (rhymes with "pass") was a prolific producer that self-pollinated, its knobby black skin easy to peel, its flesh rich in the oil that gives an avocado its flavor punch. It was a runaway hit with growers and eaters.

But even as commercial farming became beholden to the Hass, the whole Hass and nothing but the Hass, avocado scientists and hobbyists were coming up with new varieties and preserving old ones so that, on the sprawling acres of the University of California's South Coast Research and Extension Center in Irvine, you can now see more than 150 species.

The long hallways of trees at the station are as familiar to volunteer Julie Frink as her own home, some occupants more dear than others. "Every tree has its fault, and every tree has something special about it," she says. But why so many? Why not stop at Hass? Because no one knows, she says, with an Old Testament intonation, what plague is around the corner; a super thrips or mighty mite or some other ungodly pest that will take out one of the state's most important crops.

"We're banking for the unknown," she says.

Besides, there are trees here that would be perfect urban dwellers, starting with the Holiday, which grows to about 12 feet -- practically a dwarf in avocado-dom. Its waterfall canopy makes a perfect hide-out for child or adult. No wonder Frink has nicknamed it the Clubhouse. And can you believe the size of the fruit on this little guy? Green globes bigger than a fist.

For decades scientists had hoped to develop a true dwarf avocado that would give the teeny-tiny citruses -- the new garden gnomes -- some competition. Never happened. There is a tree called the dwarf Littlecado, but it's something of a misnomer: It sprouts even higher than the Holiday, about 15 feet. At least it's a wasp-waisted 10 feet wide. Its flavor isn't as tasty as the equally svelte Reed, which Frink recommends as an alternative to Italian cypress for creating a hedge.

After touting the Reed, Frink zigzags over to a Nimlioh, whose branches arch out like Chinese fireworks and whose fruit is as large and round as a small cantaloupe. Eric Focht, a research associate from UC Riverside, the Harvard of avocado science, has given this specimen a buzz cut.

"We don't always follow the pruning guidelines," he says, but the fruit-heavy tree doesn't seem at all offended.

Although retail nurseries carry the Reed, Littlecado and Holiday, they won't have the Nimlioh. Same goes for the Helen, a busty green fruit that peels as easily as a banana, and the Queen, with fruit like squash that can weigh in at 2 1/2 pounds. Nor the Jan Boyce, the "connoisseur's avocado," says Frink, who's been showing off these trees not to frustrate but to preview what will be at the Fullerton Arboretum's Green Scene sale in April, a rare chance to get the rarer trees.

Frink struggles to put into words how much she cares for the Jan Boyce. "There's nothing like it," she says. Focht cuts one open, revealing the tiny seed, the size of a large marble.